1. Field of the Invention
This invention relates to antennas for use in wireless communications; and more particularly, to an antenna with proximity sensor function.
2. Description of the Related Art
Proximity sensors are in use in commercial wireless devices as well as other product groups, and are used for a wide variety of applications. For example, it is common for a proximity sensor to be integrated into a cell phone, with the proximity sensor used to sense when the display region of the cell phone is in close proximity to an object. This sensing of an object close to the display is used to reduce battery power consumption by turning off or down the brightness of the display when the display is in close proximity to a user's head or the display is covered by an object. Another application of a proximity sensor is to integrate the sensor into a Tablet computing device and use the sensor to sense proximity of the user's body to the Tablet. When the user's body is close to the Tablet, the transmit power of the cellular transceiver is reduced to allow the Tablet to meet requirements for specific absorption rate (SAR).
One implementation of a proximity sensor is a capacitive sensor, and is effectively a parallel plate capacitor. A dielectric material is positioned between the two plates to provide support and maintain a set separation distance between the plates. Two conductors are used to connect the two plates to a circuit that monitors capacitance. As objects are placed in proximity to the capacitor the objects interact with the fringing electric field emanating from the region between and external to the plates. This interference with the fringing fields of the capacitor translates into a change in capacitance.
Multiple proximity sensors can be integrated into a device and used to provide more information on the environment and changes to the environment. Multiple problems arise in integrating proximity sensors into a device such as finding volume for the proximity sensors, incurring the cost of the sensors, and positioning the sensors at locations that are desirable, such as close to the antenna system.